False twisting of yarn

ABSTRACT

A process is described for false twist texturing a synthetic multifilament yarn by friction twisting means wherein the bleeding of real twist through the false twisting zone is arrested, thereby eliminating a source of yarn streaking in dyed goods produced from said yarns. The process involves sequentially passing multifilament yarn to be textured through a heated zone, a cooling zone, a false twisting zone, and a yarn separation zone to a take-up zone, wherein friction twisted yarn is backed up in the twisted state into the heated zone wherein it is heat set, passed through a cooling zone and hence through said friction twisting zone where the yarn is untwisted to substantially remove twist and hence through a yarn separation zone wherein the yarn is separated into at least two plies, thereby arresting twist prior to taking up the yarn.

United States Patent Doschko et al.

[ Feb. 4, 1975 FALSE TWISTING OF YARN [76] Inventors: Werner Doschko, 6901 Nussloch am Leaimbach 16; Heinz Gilch, 6908 Wiesloch in der Bohn 19, both of Germany 22 Filed: Oct. 16, 1972 21 Appl. No; 274,008

[30] Foreign Application Priority Data July 21, 1971 Great Britain 34185/71 [52] US. Cl. 57/157 TS, 57/34 HS [51] Int. Cl D02g H02 [58] Field of Search 57/34 HS, 157 TS, 157 MS [56] References Cited UNITED STATES PATENTS 2,890,568 6/1959 Willens 57/34 HS X 3,261,156 7/1966 Kunzle et al.... 57/34 HS 3,298,169 l/1967 Comer 57/157 R 3,327,462 6/1967 Wyatt 57/34 HS 3,413,796 12/1968 Comer et al. 57/34 HS X 3,423,924 1/1969 Comer et al. 57/34 HS X 3,643,412 2/1972 Maeda 57/34 HS 8/1972 Neveux 57/157 TS X 8/1972 Smith 57/34 HS [57] ABSTRACT A process is described for false twist texturing a synthetic multifilament yarn by friction twisting means wherein the bleeding of real twist through the false twisting zone is arrested, thereby eliminating a source of yarn streaking in dyed goods produced from said yarns. The process involves sequentially passing multifilament yarn to be textured through a heated zone, a cooling zone, a false twisting zone, and a yarn separation zone to a take-up zone, wherein friction twisted yarn is backed up in the twisted state into the heated zone wherein it is heat set, passed through a cooling zone and hence through said friction twisting zone where the yarn is untwisted to substantially remove twist and hence through a yarn separation zone wherein the yarn is separated into at least two plies, thereby arresting twist prior to taking up the yarn.

6 Claims, 2 Drawing Figures PATENTEDFEB j I 3.863.434

' sum 10F 2 PATENTEDFEB 4191s I 3.863.434

SHEET 2 UF 2 FALSE TWISTING OF YARN The present invention relates to a process for the false twisting of yarn. False twisting is a technique which is used to produce a texturised effect in yarns and a false twist is achieved by first passing a moving yarn through a region where it is heated to above the second order transition temperature of the materials from which the yarn is made, subsequently cooling the' yarn and then twisting the cooled yarn. The twist imparted to the cooled yarns runs back along the yarn in the opposite direction to that in which it is travelling into the heating zone and the twist is set in the yarn when it moves into the cooling zone and the temperature drops below the second order transition temperature. After the yarn has passed through the twisting device it is allowed to untwist so that the untwisting of the yarn which has been set in its twisted state results in a texturised or bulked yarn.

The bulk in the finally texturised yarn is mainly dependent on the twist density of the yarn in the heating zone. By twist density we mean the number of twists per unit length in the yarn. Twist density is controlled by the nature and physical properties of the yarn supplied, ie., its chemical type, titre, number of filaments in the cross section and by the physical properties of the filaments, and also by the imposed processing conditions, namely yarn speed, twisting speed, time and temperature of heating and cooling and by frictional forces in the twisting device.

Various devices are known for imparting twist to a moving yarn. In one such device the moving yarn is passed around a member which is provided within a rotating hollow spindle and which rotates with the spindle. in this way twist is inserted in the yarn as it passes through the spindle. This process, however, suffers from the disadvantage that only one twist may be inserted in the yarn for each rotation of the spindle and thus the amount of twist that may be inserted is limited by the maximum speed of rotation of the spindle. It is well known that this problem may be overcome by using the friction twist principle in which the yarn is twisted by contact with a rotating friction surface. The twist devices which use the friction principle generally consist of rotating hollow cylindrical bodies whose surfaces, or parts thereof are friction surfaces with which the moving yarn makes contact. In some such devices the yarn passes through the cylindrical body whereas in others the yarn enters and leaves the body from the same side and is held against the friction surface by a yarn guide.

One problem that is encountered with the friction twist principle is that of Twist Bleeding which results in occasional lengths of yarn having improperly some residual twist following detwisting. Such twist bleeding which is randomly distributed within yarn from one processing position and between yarns from different processing positions is highly undesirable as it results in streaks in the resultant fabric. Twist bleeding is thought to arise from the yarn slipping as it passes over the friction surface. In an ideally perfect false twist process the moving yarn and the twisting device are in equilibrium and the twist inserted in the yarn between the twist device and the yarn feed is constant. Further, once this equilibrium position has been reached the movement of the friction device will have no effect on the yarn after it has passed through the device but will retain the yarn in its twisted state between the device and the feed roll. However, if the frictional conditions between the yarn and the friction surface change as the yarn passes over the friction surface this equilibrium position is destroyed and it is not possible to obtain yarn having constant twist. It is this phenomenon which produces undesirable twist beyond the twist unit and is known as twist bleeding.

The present invention is therefore concerned with the friction false twist principle and is aimed at overcoming the disadvantage of twist bleeding to produce yarn having a comparatively high and constant twist level.

According to the present invention we provide a process for the production ofa texturised yarn by the false twist principle comprising passing a moving composite yarn through a zone where it is heated to a temperature above its second order transition temperature, then through a cooling zone, then to a friction twisting device and subsequently to a take off station wherein the yarn is separated into at least two plies between the twisting device and the take off station.

The term composite yarn is used to describe a yarn consisting of two or more plies. The yarn may itself by a multifilament yarn which is separated into smaller bundles of filaments after it has passed the friction twist device alternatively the yarn may be two or more separate yarns which are plied together before they pass through the friction twister. These yarns may themselves by multifilament yarns. We have found that by separating the composite yarn into at least two plies between the twist device and the take off means any twist produced beyond the twist device due to twist bleeding will be arrested at the point of separation and will run back from this point through the twist element and into the heating zone. It is not necessary to separate the yarns into the same components as were used to form the composite yarn. For instance, if two multifilament yarns are twisted together they may be separated into two yarns containing different numbers of filaments from the starting materials. Similarly, when the starting yarn is a single multifilament yarn it is not necessary to separate the yarn into bundles containing equal numbers of filaments.

The yarn used in the process of the present invention may be any thermoplastic synthetic yarn which when heated to above its second order transition temperature while in its twisted state becomes set in its twisted configuration. The techniques of the present invention may be applied to drawn yarn, to processes in which the yarn is drawn and twisted simultaneously and to processes in which the yarn is twisted immediately after drawing. The present invention is particularly useful in the production of texturised yarns from Nylon 6, Nylon 6:6, polyacrylonitrile and polyesters.

The yarn may be fed directly from the feed roll through the heater zone which in certain embodiments of the invention is also the heater zone used in conventional false twisting processes and a standard type of plate heater is particularly convenient. Similarly the cooling zone which is necessary to ensure that the yarn is cold when it passes through the twist device may be a cooling zone of the type generally used in conventional false twist processes. It may be necessary to provide cooling plates which direct cold air onto the yarn but generally we find that the distance the yarn must travel between the heater and the twist device is sufficient to cool the yarn.

The yarn is generally cold when twisted and the twisting device may conveniently be any of the known devices for imparting twist to yarns by the friction principle, in particular the twist bushes such as those described in British Pat. Nos. 797,051 and 801,335; British Pat. No. l,l97,703.

Our preferred technique is to twist together two separate yarns and subject the yarns so twisted to the friction twist principle and then to separate the two yarns after they have passed through the friction twist device. In this way the point at which the two yarns are separated provides the position at which any twist imparted by the twist device is arrested. It is already known to produce texturised yarns by twisting two yarns about each other and passing the twisted yarns through a heating zone and then a cooling zone to set the twist in the yarn, separating the yarns and, detwisting each one to produce texturised yarns. This technique has the advantage that the amount of twist in the yarns as they pass through the heating zone is constant. However the disadvantage isthat the process cannot be operated at high yarn rates or high twist density because there is a large build-up of twist at the point where the yarns are separated which requires high forces to separate the yarns, and these high forces tend to pull out some of the twist that has been inserted in the yarn and tend to produce deformations and sometimes breakages of the yarn. Furthermore, the amount of twist that can be inserted in the yarn is limited by the amount by which the two yarns can be intertwined. The present invention however enables this type of twist principle to be used to produce yarns having a higher degree of twist because in our process the twist density in the heating and cooling zones is the combination of the twist inserted by the twist device and the intertwisting of the yarns whereas the twist density at the point where the yarns are separated depends only on the twist due to intertwisting and any twist due to slippage of the yarn through the twisting device. Thus high constant twist in the heating and cooling zones may be achieved at the same times as low twist density at the separator.

In the process described above where two or more yarns are texturised together the device which separates the yarns may be a pin having a wear resistant surface such as ceramic or chrome surface.

The present invention is illustrated but in no way limited by reference to the accompanying drawings in which FIG. 1 is a diagrammatic illustration of a process in which two yarns are treated simultaneously and FIG. 2 is a diagrammatic illustration of the treatment of a single multifilament yarn.

Referring to FIG. 1, two yarns 3 and 4 are withdrawn from the bobbins l and 2 and fed to the delivery roll 8 by means of the yarn guides 5,6 and 7. The delivery roll 8 feeds the yarns 3 and 4 into the heating zone 9 then through the cooling zone 10 to the twisting device 11. After the yarns have passed through the twist device 11, they pass over the freely rotating pulleys l2 and 13 to the delivery roll 14 after which they are allowed to untwist to produce texturised yarns which are wound on the package 15.

Referring to FIG. 2, yarn 16 is withdrawn from bobbin 17 onto the delivery roll 18 via the yarn guide 19. The yarn then passes into the heating zone 20 and the cooling zone 21 and then through the twist device 22. The filaments of the yarn are separated by passage over the pin 23, then re-united and finally fed to the wind up package 24 by means of the delivery roll 25. In this technique the pin 23 prevents the twist from running from the twist device 22 to the delivery roll 25.

The present invention is further illustrated but in no way limited by reference to the accompanying examples.

EXAMPLE 1 Two supplies of drawn Nylon 6:6 yarn each of 22 decitex and each containing 7 filaments were texturised in an apparatus of the type illustrated in FIG. 1. The yarns were fed at a speed of metres per minute and the twisting device consisted of a hollow cylinder the internal surface of which provided the friction surface and was rotating at 2,412 revolutions per minute. The two yarns were twisted around each other by the action of the false twist unit and separated after passage through the twist unit by the pulleys 12 and 13.

A yarn having a high degree of texturising which was uniform along the length of the yarn was obtained.

EXAMPLE 2 A single Nylon 6:6 yarn of decitex 220 containing 20 filaments was subjected to the process illustrated in FIG. 2. The friction twist device 22 was rotated at 4,825 revolutions per minute and the yarn was divided in two separate yarns by the pin 23.

As with Example 1, a yarn having a high degree of texturizing which was uniform along the length of the yarn was obtained.

We claim:

1. A process for false twist texturing a synthetic multifilament composite yarn comprising forwarding a yarn to be textured from feed means sequentially through a heated zone, a cooling zone, a false twisting zone and a yarn separation zone to a take up zone, friction twisting said yarn in said false twisting zone and passing said twist in said yarn through said cooling zone into said heating zone wherein said twist is heat set, cooled and untwisted as it is forwarded through said false twisting zone to thereby heat set the imposed twist and subsequently untwist to substantially remove real twist, separating said yarn into at least two plies to thereby arrest any residual real twist recombining the plies and taking up said yarn in said take-up zone.

2. A process according to claim 1 in which the composite yarn is a single multifrlament yarn.

3. A process according to claim 1 in which the composite yarn comprises two or more separate yarns which are plied together before they pass through the friction twister.

4. A process according to claim 1 in which the yarn is drawn at the same time as it is twisted.

5. A process according to claim 1 in which the yarn is twisted immediately after drawing.

6. The process of claim 1 wherein separated plies of yarn are taken up as separate yarns. 

1. A process for false twist texturing a synthetic multifilament composite yarn comprising forwarding a yarn to be textured from feed means sequentially through a heated zone, a cooling zone, a false twisting zone and a yarn separation zone to a take up zone, friction twisting said yarn in said false twisting zone and passing said twist in said yarn through said cooling zone into said heating zone wherein said twist is heat set, cooled and untwisted as it is forwarded through said false twisting zone to thereby heat set the imposed twist and subsequently untwist to substantially remove real twist, separating said yarn into at least two plies to thereby arrest any residual real twist recombining the plies and taking up said yarn in said take-up zone.
 2. A process according to claim 1 in which the composite yarn is a single multifilament yarn.
 3. A process according to claim 1 in which the composite yarn comprises two or more separate yarns which are plied together before they pass through the friction twister.
 4. A process according to claim 1 in which the yarn is drawn at the same time as it is twisted.
 5. A process according to claim 1 in which the yarn is twisted immediately after drawing.
 6. The process of claim 1 wherein separated plies of yarn are taken up as separate yarns. 